1. Field of the Invention
The present invention relates to organic chemistry in which organics are synthesized in minute amounts of samples and biochemistry in which a PCR (polymerase chain reaction) method or the like is conducted, particularly to a microchip (μTAS: Micro Total Analysis System) into which functions of analyzing components of liquids, pretreatment functions, and the like are integrated, and also to a reaction processing method.
2. Description of the Related Art
Micro multi-chamber devices are used as small reactors used for biochemical analysis and usual chemical analysis. Such devices use, for example, microwell reaction well plates such as microtiter plates in which a plurality of wells are formed as reaction wells in a planar plate surface (see Japanese Patent Laid-Open No. 2005-177749).
When a minute amount of a liquid sample is handled, sampling of the liquid sample or sample addition is typically performed using a micropipettor.
In that case, since the sample reaction site is open, there is a fear that a foreign matter may be mixed into the sample from outside. Moreover, the sample might contaminate the outside environment. It is desired that a sample be treated in the device to prevent a foreign matter from mixing from the outside and prevent outside environmental pollution.
In addition, it is desirable to increase the number of reaction wells that are integrated in the plate surface to further improve the efficiency of analysis using such a micro reactor. However, when the number of reaction wells is increased, it is difficult to equally distribute samples into each reaction well.
Hence, the present inventors propose a passive sample introduction method in which a plurality of reaction wells are formed in a base body and liquid samples can be equally dispensed thereinto (see M. Kanai, et. al. “A Multi Cellular Diagnostic Device for High-throughput Analysis”, Proceeding of μTAS2004, pp. 126-128, 2004). The word “passive sample introduction method” means that a liquid sample flowing in a channel is dispensed by branching the channel stepwise without giving force or energy interacting with the liquid sample flowing in the channel to the sample from the outside.
Additionally, a structure of weighing out a small amount of a liquid that can quantitatively treat a small amount of a liquid is provided. The structure includes a first channel, a second channel, a third channel opened in the channel wall of the first channel, and a fourth channel opened in the channel wall of the second channel, connecting one end of the third channel to the second channel and weakening capillary attraction thereon as compared with the third channel (see, e.g., Japanese Patent Laid-Open No. 2004-163104 and Japanese Patent Laid-Open No, 2005-114430). According to the structure of weighing out a small amount of a liquid, a liquid introduced into the first channel is drawn into the third channel. Then the liquid remaining in the first channel is removed, and a liquid of a volume corresponding to the volume of the third channel can be weighing out by the second channel.
However, when a small amount of a liquid sample is transferred to a reaction well and the amount of the liquid sample is as minute as 10 μL (microliter) or less, once the liquid sample is contacted with the ceiling of the reaction well (plate surface disposed opposite to the reaction well), the weight of the liquid droplet is so small that the droplet cannot fall by gravitation, whereby the liquid sample may remain sticked to the ceiling of the reaction well without falling.
FIG. 24 is a schematic sectional view that shows a conventional micro droplet operation device. FIG. 24 shows a state when a liquid sample 30 is injected into a reaction well 5 from a liquid introduction channel 12a formed between a base plate 3 and a cover plate 11. As shown in FIG. 24, when the weight of the liquid sample 30 is very small, a droplet of the liquid sample 30 attaches to a side wall or the ceiling of the reaction well 5 and thus the sample may not sufficiently react with a reagent (not shown) present at the bottom of the reaction well 5.